The present invention relates to a method for the preparation of an organopolysiloxane having two hydrogen atoms directly bonded to the same silicon atom at the molecular chain end, which is referred to as an .omega.,.omega.-dihydroorganopolysiloxane hereinbelow, or, more particularly, to a method for the preparation of an .omega.,.omega.-dihydroorganopolysiloxane free from the problem in the prior art method due to the acidic or basic by-product produced by the reaction.
As is well known in the art of silicones, .omega.,.omega.-dihydroorganopolysiloxanes are reactive and useful as an intermediate for the synthesis of various kinds of organosilicon compounds and as an ingredient in organopolysiloxane compositions, e.g. cellular foamed bodies of organopolysiloxane compositions, curable by the irradiation with actinic rays, e.g. ultraviolet light, or by the mechanism of so-called hydrosilation which is a reaction between silicon-bonded hydrogen atoms and aliphatic unsaturation in the other constituent in the composition.
Such an .omega.,.omega.-dihydroorganopolysiloxane is synthetically prepared in the prior art by the method disclosed, for example, in Japanese Patent Publication No. 45-9474, according to which a dihydro monohalogeno silane of the general formula RSiH.sub.2 X, where R is a monovalent hydrocarbon group and X is a halogen atom, acyloxy group or amino group, is mixed with an organo-silicon compound having a silanolic hydroxy group such as an .alpha.,.omega.-dihydroxy diorganopolysiloxane of the general formula HO--(--SiR.sub.2 --O--).sub.n --H, in which R has the same meaning as defined above and n is a positive integer, so that a condensation reaction takes place between these two reactants to form a linkage of RH.sub.2 Si--O--SiR.sub.2 -- at each of the molecular chain ends with formation of HX, such as a hydrogen halide, carboxylic acid and amine, as the by-product.
The above mentioned conventional method for the preparation of an .omega.,.omega.-dihydroorganopolysiloxane is sometimes disadvantageous because the by-product HX can be removed completely from the product only by a very troublesome and time-consuming purification process while even a trace amount of such an acidic or basic impurity is very detrimental in certain applications of the .omega.,.omega.-dihydroorganopolysiloxane.